


A Lesson in Bones

by Magichorse



Category: The Locked Tomb Trilogy | Gideon the Ninth Series - Tamsyn Muir
Genre: Bodyswap, Canaan House, F/F, Gideon tries necromancy, bones gone wild, it goes how you think it might, tltexchange2020
Language: English
Status: Completed
Published: 2021-01-03
Updated: 2021-01-03
Packaged: 2021-03-11 02:21:16
Rating: Teen And Up Audiences
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,810
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28417539
Author URL: https://archiveofourown.org/users/Magichorse/pseuds/Magichorse
Summary: One of the laboratory trials at Canaan House compels Harrowhark to swap bodies with her cavalier, unexpectedly giving her vast necromantic powers to her untrained counterpart. What will Gideon do with the power of the most talented bone adept in generations at her disposal? Nothing good, probably.Written for the Locked Tomb Holiday Exchange 2020.
Relationships: Gideon Nav/Harrowhark Nonagesimus
Comments: 8
Kudos: 70





	A Lesson in Bones

**Author's Note:**

  * For [Jessiuss](https://archiveofourown.org/users/Jessiuss/gifts).



> For Jessiuss! The prompt I selected was "body swap." Rather than continue the body swap shenanigans of HtN, I went back to Canaan House and had a bit of fun with the idea of Gideon getting the chance to sling some bones around. Why should Harrow have all the fun?
> 
> CW for minor injuries.

“Undo this. Right. Now."

“Griddle, you’re overreacting,” replied Harrowhark dismissively to the fuming cavalier at her back.

“Uh, no I'm not," said Gideon indignantly, "This is some real bullshit, Nonagesimus. I need you to put us back like, _five minutes ago._ ” She disliked the obvious tinge of desperation creeping into her words, but liked the sound of her words coming out in Harrow’s voice even less.

Harrowhark turned her head and looked _down_ at Gideon, which was easy to do, because she had just minutes before tapped Gideon on the forehead and, through some creepy, messed-up, necromantic hocus pocus, _switched their fucking bodies._ Gideon stood there tensely, looking up at Harrow inhabiting the frame Gideon had spent a lifetime toning to perfection. Easy for her necromancer to be casual, she thought, _she_ was the one in the hot body. Gideon, by comparison, felt small and frail and horribly vulnerable.

“If you want to switch back so badly, then stop whining and let me concentrate," said Harrow, putting down the empty box where the laboratory room's key would have been, had they been the first pair to complete this trial. Clearly, the prize had already been taken, but that hadn't stopped Harrow from searching fruitlessly over every inch of the room. "I do not like this either," she added.

The laboratories beneath Canaan House were layered down deep into the rock, their corridors of steel and sputtering lights descending to depths yet unexplored. All of them were dangerous, and all had been left in pristine condition for future generations of necromancers to break themselves upon like the waves against the cliffs outside. There was no giant monster to fight here, or physical pain to endure, but Gideon didn’t like this room, innocuous with its small bookshelf of necromantic texts and stand of rapiers, any more than the others. 

Across the room, Harrow had turned her attention to Gideon’s hands. She flexed the fingers and turned them over and back before pulling Gideon’s rapier experimentally from the sheath and giving it a ridiculous little swish.

“I’ll admit I don’t know the point of this exercise exactly, even if I’ve executed the theorem,” said Harrowhark as she moved the tip of the rapier through the air, “But I believe we’ve done it. It’s not as good as getting a key, but it will give us a clue to the whole. So, I will direct you on how to put us back.”

“Wait, I have to do it?”

“Yes, you are presently the necromancer.”

That pulled Gideon up short. She had been so focused on her diminished height and build, not to mention the absolute mindfuck it was to be staring at her own body from the outside, to notice anything else. She froze, and when she stood perfectly still, she could feel a whisper of power circulating through her—Harrow’s—body.

“Oh,” was all Gideon could manage, mimicking Harrow’s earlier action and staring down at the small, gloved hands which were currently under her control. She twitched the fingers experimentally, wondering how it worked. She’d seen Harrow work necromancy any number of times. Surely she could figure it out. “So I can, like, make bones grow now?”

“The only thing you’re going to do is listen closely to my instructions on how to put us back, and then you’re going to perform them precisely as directed.”

“Like hell I am,” said Gideon, suddenly warming to the idea that she was in possession of a necromancer’s power. Her head filled with all the times in her life Harrow had torn at her with skeletal hands, or pinned her under a hail of shards, or crushed her beneath towering constructs. She began to draw Harrow’s thin lips into a wicked grin.

The warning glint in Harrow’s eyes was unmistakable even in Gideon’s face. 

“Griddle,” she said coldly, “I am not being immodest when I say I have a tremendous amount of power at my disposal. It would be idiocy of the highest order for you to even attempt to direct it. You couldn’t even begin to fathom the consequences of... are you listening to me?”

Gideon was not listening to Harrow. She was fishing enthusiastically around in Harrow’s pockets for a piece of bone suitable to her purpose. Her fingers closed on a small cube of carpal and she held it up to her face to squint at it, trying to see if it looked any different with a necromancer’s sight. She thought it might have the same glow she had seen at the joints of the regenerating bone construct, but that turned out not to be the case. However, even though she did not see a difference, she _felt_ one. 

Through the gloves that Harrow wore, where fabric met bone there was…something. A lack of something, to be precise. An emptiness in the weave of the bone that pulled gently at her power. Gideon turned the carpal over and over between her fingertips, marveling at it. As she focused, she slowly became aware also of the studs lining Harrow’s ears and the bangles at her wrists, all quiescent but unmistakably alive to her senses. Gideon had never had cause to appreciate a single bone in her entire life, but all of a sudden, she was absolutely enamored.

Across the room, Harrow had gone very, very still.

“Nav,” she said, drawing her name out slowly in a warning tone that did not entirely hide the thread of fear underneath, “Don’t you even think of—”

But her use of Gideon’s name had broken her cavalier’s reverie, and before she could finish the order, Gideon had tossed the bone into the air, as she had seen the Reverend Daughter do thousands of times before. It sailed away from her in a perfect arc toward the ground. She could still sense it as it moved away from her, though the connection waned noticeably with distance. Before it struck the earth, she released a bit of the power she felt circulating in her body into the waiting vessel of bone. There was the slightest twinge at her temples as the energy expenditure took its toll, but the effect on the carpal was instantaneous. The bone puffed out like a popcorn kernel introduced to heat, doubling unevenly in size, and landed with a satisfying _plink!_ on the laboratory floor.

Both of them stared at it in silence, Gideon in wonder and Harrow with tense shoulders. After a few heartbeats of nothing, Harrow audibly let out the breath she was holding.

“I hope your foray into necromancy was satisfying, Nav, now it’s time to put things back.”

Gideon looked at the little bone-puff on the ground. It was still connected to her, she could tell. Experimentally, she let a little more energy flow into the bone, huffing slightly at the same twinge of pain as her body created the necessary thanergy through a small die-off of living cells. The surface of the distorted carpal rippled, and then a thin, blade-like protrusion the size and shape of a paring knife sheared out of the side.

“Whoah!” said Gideon, delighted with this turn of events.

“What?” said Harrow, and then looked down at the bone and its new sharp appendage.

“It’s like a little bone-knife!”

“Stop it, you don’t know—”

Gideon released more energy into the bone, and this time she felt the toll of the power bite deep as her body sacrificed healthy tissue to feed the demands of the magic. She broke out instantly into a sweat and she somehow did not doubt it was tinged with red.

The effect on her experimental construct was immediate and pronounced. The bladed protrusion shot out another foot, but that wasn’t all. The irregularities she had introduced to the surface of the bone in the initial burst erupted into long, thin spikes. Jolted by the growth, the bone nucleus flipped into the air, spinning as spears of bone tore from its sides, racing outward toward the walls.

Harrow, with the benefit of Gideon’s reflexes, spun herself sidelong to the spines and avoided being skewered through her gut. Gideon, however, was working with a frailer body that was already being taxed by the demands of thanergetic power. She tried to duck beneath a spike that raced toward her chest, but only made it far enough to avoid a bone shard through her lungs, feeling a sting in her shoulder where the spike caught her instead.

“Stop it, Nav!” hissed Harrow “You’re going to get us both skewered to death.”

Gideon tried to cut the connection, but in truth was she was panicking. In response, the magic flared to her defense, burning her flesh for fuel from the inside out. The construct, looking like nothing Gideon had ever seen before, continued to split and grow in alarming, deadly spurts. The chaos of rapid-branching spikes splintered against the walls and floors and furniture in a staccato barrage.

Blood sweat began to stream down her face in earnest. Her lungs seized in a painful cough. She could taste the salt and copper of blood on her lips. And still, the power did not stop tearing through her. A few more spikes sheared her flesh as she failed to twist out of the way.

Gideon almost missed it when Harrow raised the rapier in her hand to strike at the bone spears. What her necromancer utterly lacked in technique was made up for by the sheer strength in Gideon’s arms. Harrow smashed through the field of bone spikes, which were numerous, but thin. They cracked and shattered like ice beneath the blows. Gideon only realized belatedly, as a blade flashed before her sweaty face and blurring vision, that Harrow was fighting her way towards _her_ instead of the door. Before she could protest, Harrow was in her space, dropping the rapier and grabbing for her hands. 

For a moment Gideon just looked at the small gloved hands grasped in her body’s larger ones. The violent splintering of bone faded into background noise. How delicate those hands were, she thought; how easily they fit. Then Harrow was pressing those thumbs firmly into her palms and bringing her face so close Gideon was forced to look up into her own golden eyes. Harrow held her gaze, squeezed her hands, and said, firmly, “Stop.”

The pressure on her palms grounded her, and the command cut through her panic like a ray of sun at daybreak. She stopped. The fire in her veins cooled. The bone around them went inert.

Harrow slowly let her hands go and looked around cautiously at the wreck of the room. Everywhere was littered with shattered bone or criss-crossed with spikes, but nothing else stirred. Her posture relaxed a fraction.

Gideon took a deep breath to steady herself and noticed her limbs were trembling. With effort, she stilled them. She looked down at the blood trickling from the cuts and punctures she had sustained. Surprisingly, none of them looked as deep as she had feared, though she was so sure she had seen...well, she wasn’t going to complain.

“Sorry about these,” she said, touching one gloved fingertip to a gash across her left arm. It tingled with a mix of thanergy from the torn flesh and thalergy from the blood. It felt instinctive to try to knit it together.

“Don’t you _dare_ try working flesh magic on my body,” snarled Harrowhark, “After what you just did. You have no idea what you’re doing and it’s going to get us killed.”

“So teach me something,” said Gideon, "If I'm so terrible." 

“I—you—what?” sputtered Harrowhark, twisting up Gideon’s features in rage and indignation, “You absolute _cretin!_ You have done quite enough to my body. You are going to put us back.”

“No,” said Gideon, digging in. The panic of moments ago was already fading, readily replaced by the petty delight of having Harrow at her mercy. “I’ll put us back, but those are my terms. Teach me something.”

“There is no way you’re in a fit state to perform more necromancy after that.”

“Nah, I'm fine,” said Gideon, quite truthfully. Her power already felt replenished, and now that she was looking at them again, what she could have sworn were cuts seemed closer to light scratches. She wiped the cooled blood sweat off of her face with Harrow’s sleeve.

Harrow narrowed her eyes at Gideon, which felt like being scrutinized by her own reflection. 

“I mean it. I’m not satisfied with my necromantic experience. I am a dissatisfied customer, and as long I don’t get what I want, you don’t get what you want.”

Harrowhark tried to stare her down, but Gideon didn’t flinch. Neither moved until Harrow stepped suddenly into Gideon’s personal space. Before Gideon could back away, startled, Harrowhark reached down and into the pockets of her own robe, rummaging through the items there. Gideon found it to be quite an invasive feeling to have her own body looming over her, picking through her pockets.

After a moment, Harrow pulled out a section of bone that was perhaps two centimeters long, relatively thin, and possessed of a gentle curve. It had been neatly cut at each end, as if by a blade, and Gideon guessed the rest of the pieces were also present somewhere, secreted away for emergency use in equally neat sections. 

Harrow surprised her again by reaching out, grasping her right hand, and turning it palm up in her own.

“Take this,” she said tersely, offering the fragment to Gideon with her free hand, “In your fingertips. Yes, that’s correct.”

Gideon gripped the smooth sides of the bone very carefully, feeling the empty, yearning spaces in the structure.

“Now, can you tell me what bone this is?” asked Harrowhark.

“Is this a quiz?”

“This is a lesson, Griddle. You do not get to advance unless you grasp the basics. Or did you forget what just happened?”

“Yeah, yeah,” muttered Gideon, but turned her attention back to the section of bone. She’d seen a lot of bones in her day, it didn’t take her long to narrow it down to either a clavicle or an ulna, each thin and graceful pieces in their own right. She squinted, judged, and said decisively, “Clavicle.”

“Very good,” said Harrowhark, though she didn’t sound in the least impressed, as if it was as obvious a difference as a triangle from a circle. “Your other hand, please,” she said, and gestured for it. Gideon gave it. “Hold it over the bone like this,” she said, turning it palm down to hover a few inches above the surface of the clavicle section. “This hand,” she said, covering the upper hand with her own, “will control the flow of thanergy, while this,” she said, putting a gentle pressure on the one which gripped the bone, “will inform the structure. Start with building out to the shorter end, the sternal extremity. Show me which end that will be.”

Gideon frowned, concentrating. She tried to feel the structure for clues, but the information feedback she was getting made no sense to her, she didn’t have the knowledge or experience to interpret it. She willed it with her mind to reveal its secrets. It kept its silence.

“I…don’t know,” said Gideon, certain she was going to be met with a triumphant sneer and mockery. Harrow did neither. She manipulated the hand that gripped the bone so that one end was facing away from Gideon and gave it a tap, “This one.”

Gideon chewed her lip and realized that she was, despite her bravado, nervous after what had happened. She glanced up at Harrow, but the other girl's attention was focused entirely on the section of clavicle held in her body’s gloved hands, expression tense, but no longer angry. 

Gideon flexed the hand that was suspended above the bone nervously, and then released the tiniest bit of thanergy into the structure. The change was almost visibly imperceptible, but she could feel the bone building slowly at a cellular and mineral level. After a few seconds of this, with no disaster occurring, she increased the flow. At a controlled pace, she found, the outflow of thanergy produced only a steady heat, not pain.

Harrow kept her hands on Gideon’s, guiding, and surprisingly gentle. Gideon searched deep in her memory. Had she ever seen Harrow’s parents move their daughter’s hands so tenderly? She couldn't imagine it. The Reverend Father and Mother never seemed to touch her except to correct or to reprimand. Was Harrow teaching her, then, as she wished she had been taught? The thought made her uncomfortable, so she abandoned it and turned her attention back to the bone. She let her concentration sink completely into her task, so she nearly jumped when Harrow spoke.

“The bone will recall itself,” said her necromancer, as if in recitation, “Allow it to become the shape it used to be. This bone was once part of a whole, and it remembers.” She paused and Gideon saw a very slight frown form on her face. “You don’t need to add the marrow for this exercise,” she said.

“That’s the easiest part,” said Gideon truthfully. The marrow had freely and dutifully formed in the hollow of the bone as she built. Harrow said nothing to this, just let her build millimeter by millimeter and taper the bone to its natural terminus, so by the end she was holding fully one third of a human clavicle. Gideon flipped the bone around so the unfinished end was repositioned outward, and with much more confidence and efficiency, pulled from the bone the familiar arch and the rounded end of the acromial extremity. In a few minutes she had a complete, smooth, beautiful clavicle.

She took in her handiwork, turning the bone over and over in her hands, and then her face broke into a wide grin. From the feel of it, Harrow’s facial muscles had never been taxed in this way. She looked up at Harrow—at her own face— and beamed for all she was worth.

“Ha!” said Gideon, “Who’s the bone prodigy now?”

“Oh, please,” huffed Harrow.

“Come on! I did a good job! I made a whole bone! Just look at it!”

“Honestly, Griddle, I can’t tell the level of the craft without my necromantic senses, but I’m quite sure it’s nothing to write home about.”

“Are you kidding? I am going to keep this and put it on my future mantle with a plaque that says ‘GIDEON NAV MADE THIS.’ When has a cavalier ever made a bone? I’ve got to be the first.”

“Exactly. No one is ever going to believe you. Now, you’ve had your lesson, you’ve made a bone, it’s time to put things back in order.”

“Fine, fine,” said Gideon. Now that she had completed the task she remembered that she was in a tiny, frail, husk of a body and longed to get back to her usual badass self. She placed a fingertip on Harrowhark’s forehead, as she had seen her necromancer do at the outset.

Her senses were immediately assaulted by the sounds of a human body’s discordant processes—blood rushing, lungs expanding, heart crashing, and a hundred other sounds. She yanked her hand back and said, “Sweet, merciful Prince Undying, it’s so _loud!_ ”

Harrow stared at her for one long moment before raising her eyebrows and giving something that sounded like a snort and then, miraculously, a small smile.

“I told you that during the combat trial,” she said, plainly amused, “You’re a cacophony. Now you understand.”

Gideon stood dumbstruck. Harrow was smiling at her. The shock of it gave way slowly to something else, and she felt herself returning the smile. A small feeling fluttered in her chest as she realized that she did, for once, understand her necromancer. They stood there, sharing their private moment, neither disturbing the silence until Harrowhark seemed to recall herself. 

“It’s time to put us back, Nav,” she said, breaking eye contact as if embarrassed, “Just open the connection, our spirits will be wanting to return to their proper bodies, it won’t take much effort.”

Gideon nodded and once again placed a fingertip to her own body’s forehead, this time forewarned of the noise. As Harrow had described, as soon as she conceptualized a channel between them, the world dimmed briefly and spun, and then she was looking down at Harrowhark, skull-faced and pointy as ever.

Gideon stepped back and looked herself over intently. She gave her arm muscles a good flex. It felt great; everything was in working order. She looked over to check on her necromancer, who was still holding the bone Gideon had labored so hard to make, apparently checking over the work.

“Alright, hand it over,” said Gideon, reaching out to take her craft project.

Harrow’s head snapped up from where she had bent it low to examine the bone. She looked, of all things, surprised.

“What’s that look for?” frowned Gideon. “I just said I wanted it for posterity.”

Harrow stared at her mutely and made no move to hand it over. Gideon waited patiently for a few moments before frowning, annoyed.

“Come on, Nonagesimus, you already have every other bone in Canaan House that isn’t walking around as a skeleton. I made that one fair and square!”

Harrow just continued to stare at her with wide, dark eyes. Her lips twitched once or twice, as if she wanted to speak, but couldn’t find the words.

Gideon slumped her shoulders in a show of exasperation, and groaned, “Fiiiine, you can hold it for now. But I want it back later.” Already moving on with her life, Gideon realized she was hungry. It was well past dinner time. “Come on, let’s go, bone mistress,” she said, and hauled open the heavy metal door that lead to the hallway.

* * *

Alone in the laboratory, Harrow listened to the retreating sound of Gideon’s boots. In her hands she clutched a clavicle that positively hummed with thalergetic energy, the marrow warm and thriving at its core. Gideon had created _living bone,_ a feat which was beyond even Harrow's talents. All of her skill was for manipulating and animating that which was dead. It should have been impossible, but in her hands lay the proof, like a tiny miracle.

The mystery was going to have to wait for another day, she knew. Once she achieved lyctorhood— and there was no question in her mind that she would— there would be so much more she understood. She was depending on it.

She opened her robes and slipped the bone carefully into an inner pocket. When she redid the fastenings, the bone came to rest over her heart, nestled warmly against her chest. She placed a hand over it briefly, and then followed after her cavalier.

**Author's Note:**

> Thank you for reading : )


End file.
